since stocks started selling in may, it's lost nearly half of its predebut value. >> mark zuckerberg is not an advertising guy. he's reluctant to make facebook a place where advertisers thrive and users don't. but at a certain point, this is the balance that facebook has to juggle. >> reporter: what users may not like is reports that the company is studying how its online ads later affect how users buy offline. >>> we're going to get to the heartwarming comeback story now. adam greenberg of the marlins suffered a devastating injury in his first major league at-bat. but last night, he scored big with the fans. abc's matt gutman was there. >> reporter: those roars, the standing ovation, all for this man, adam greenberg. not because he's a star. but because he is proof second chances really do happen. >> hearing my name and my number, it's a dream come true. >> reporter: it took greenberg seven years to get his second big league at-bat tuesday. >> here we go. >> reporter: a small moment, perhaps. but for the 31-year-old, this was his real-life "field of dreams." that's because greenberg